English verb conjugation
COULD LENGTHEN

Regular verb: lengthen - lengthened - lengthened

Affirmation

Simple form	V-ing form
I could lengthen you could lengthen he could lengthen we could lengthen you could lengthen they could lengthen	I could be lengthening you could be lengthening he could be lengthening we could be lengthening you could be lengthening they could be lengthening
Perfect	V-ing perfect
I could have lengthened you could have lengthened he could have lengthened we could have lengthened you could have lengthened they could have lengthened	I could have been lengthening you could have been lengthening he could have been lengthening we could have been lengthening you could have been lengthening they could have been lengthening

Negation

Simple form	V-ing form
I couldn't lengthen you couldn't lengthen he couldn't lengthen we couldn't lengthen you couldn't lengthen they couldn't lengthen	I couldn't be lengthening you couldn't be lengthening he couldn't be lengthening we couldn't be lengthening you couldn't be lengthening they couldn't be lengthening
Perfect	V-ing perfect
I couldn't have lengthened you couldn't have lengthened he couldn't have lengthened we couldn't have lengthened you couldn't have lengthened they couldn't have lengthened	I couldn't have been lengthening you couldn't have been lengthening he couldn't have been lengthening we couldn't have been lengthening you couldn't have been lengthening they couldn't have been lengthening

Interrogative form

Simple form	V-ing form
could I lengthen? could you lengthen? could he lengthen? could we lengthen? could you lengthen? could they lengthen?	could I be lengthening? could you be lengthening? could he be lengthening? could we be lengthening? could you be lengthening? could they be lengthening?
Perfect	V-ing perfect
could I have lengthened? could you have lengthened? could he have lengthened? could we have lengthened? could you have lengthened? could they have lengthened?	could I have been lengthening? could you have been lengthening? could he have been lengthening? could we have been lengthening? could you have been lengthening? could they have been lengthening?

Interro-negative form

Simple form	V-ing form
couldn't I lengthen? couldn't you lengthen? couldn't he lengthen? couldn't we lengthen? couldn't you lengthen? couldn't they lengthen?	couldn't I be lengthening? couldn't you be lengthening? couldn't he be lengthening? couldn't we be lengthening? couldn't you be lengthening? couldn't they be lengthening?
Perfect	V-ing perfect
couldn't I have lengthened? couldn't you have lengthened? couldn't he have lengthened? couldn't we have lengthened? couldn't you have lengthened? couldn't they have lengthened?	couldn't I have been lengthening? couldn't you have been lengthening? couldn't he have been lengthening? couldn't we have been lengthening? couldn't you have been lengthening? couldn't they have been lengthening?